Watersheds (HUC8) for the southern Sierra, California, USA

This Watershed Boundary Dataset (WBD) is a complete 1:24,000 scale digital hydrologic unit (HU) boundary layer for the 4th level subbasin (8 digit), the 5th level watershed (10 digit), and the 6th level (12-digit) subwatershed for the state of California.This dataset consists of georeferenced digital data and associated attributes created in accordance with the "USGS National Map Accuracy Standards and the NRCS Federal Standards for Delineation of Hydrologic Unit Boundaries, 10/01/04"
(ftp://ftp-fc.sc.egov.usda.gov/NCGC/products/watershed/hu-standards.pdf).

The dataset was developed by digitizing watershed and subwatershed boundary lines using 1:24,000-scale digital raster graphics (DRG), high-resolution digital watershed datasets, a high-resolution National Hydrography Dataset (NHD) at 1:24,000-scale, and 1:250,000-scale draft hydrologic boundary lines. A 30-meter National Elevation Dataset (NED) was used to produce the 1:250,000-scale preliminary draft boundaries, as well as a hillshade layer for additional reference.
Some draft catchments (watersheds/subwatersheds) were also created with Watershed Boundary Dataset tools (ArcHydro Tools, Version 9), using the NED for terrain analysis and the NHD for determining stream flow direction.

Polygons are attributed with the following: hydrologic unit codes for 4th level sub-basins, 5th level watersheds, and 6th level subwatersheds; HU sizes (in acres); states containing the HUs; non-contributing areas; downsteam hydrologic units; 5th and 6th level names; type of HUs (standard, frontal, etc.); flow modifications; and Geographic Names Information System (GNIS) identification numbers. Lines are attributed with the highest hydrologic unit code for each (sub)watershed, linesource, and a metadata reference file.